internal/pkg: optionally exempt implementations from cures counter

This avoids holding up many slots with a long pipeline.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/archive.go

@@ -278,6 +278,8 @@ type archiveArtifact struct {
 	f Artifact
 }
 
+var _ CuresExempt = archiveArtifact{}
+
 // NewArchive returns a new [Artifact] backed by the supplied [Artifact]. The
 // source [Artifact] must be a [FileArtifact] and produce a stream compatible
 // with [Reader].
@@ -403,3 +405,7 @@ func (a archiveArtifact) Cure(t *TContext) (err error) {
 	}
 	return
 }
+
+// CuresExempt exempts the cheap [KindArchive] implementation often found at
+// the end of a [FileArtifact] pipeline.
+func (archiveArtifact) CuresExempt() {}